This invention relates to a system and method for processing signals representing sound or music having multiple amplitude and/or phase differentiated components so that when the signals are decoded they may be separated into these components and the separated components be selectively applied to acoustic transducers.
The normal experience in listening to music or sound in live performance is to receive the sound from a multitude of sound source locations, including direct and reflected sound waves. In addition, if the sound source moves there is a frequency shift corresponding to the doppler frequency shift or effect. However, when recorded music or sound is reproduced, the number of sound sources is limited by the number of available loudspeakers.
In the common systems used to this time and for which the majority of persons own receiving equipment, there are two loudspeakers or acoustic transducers spaced apart to give the effect of the music emanating from any point between the two speaker locations. But with only two loudspeakers, the listener is deprived of certain sound signal information which would be received in a live performance, and therefore some of the effect of the live performance is lost. Particularly, many cues to the distance and location and scope of a sound source are dependent upon the information received in the reverberant sound field. However, most of this field cannot be provided in a two-loudspeaker system. It is therefore desirable to provide a system whereby the sound signals are applied to at least four loudspeakers so that both the direct and reverberant sound field are present and the effect of the sound or music is of that being generated in a spacial continum. A further effect is to effectively surround the listener with sound, as though he were sitting in the middle of the performing group. But although many people appreciate the enhanced sound derived from the four speakers playing different portions of a program, most have too much invested in stereo reception equipment to be willing to replace it with equipment for receiving and amplifying four discrete sound signals.
To this end, techniques have been developed for combining or matrixing the four recorded signals into two signals in an amplitude and phase determined relationship. Ordinarily, the two signals to be applied to the rear speakers are combined into the two signals intended for application to the front speakers which remain separate so that such recordings are compatible with stereophonic equipment.